The present invention relates to a particulate absorbent, for the absorption of liquids, comprising particles selected from the group consisting of particles of glass-like polysaccharides and of particles of glass-like polysaccharides occluding, in their internal structure, at least one surfactant.
The present invention further relates to the use of the latter particulate absorbent alone or in combination with additives or intrants, as absorbent of polar liquids and of physiological fluids and more particularly relates to specific absorbent compositions of the particulate absorbent according to the invention with selected carboxymethylcelluloses and/or with selected gums.
The present invention also concerns absorbent combinations of a predetermined amount of at least one particulate absorbent and/or of a predetermined amount of at least one absorbent composition with a suitable carrier.
Various glass-like polysaccharides are known in the art. For example U.S. Pat. No. 5,360,903 describes glass-like polysaccharides and glass-like starches having a substantially occluded water component. Such polysaccharides are useful for abrading surfaces.
Diapers and more particularly sanitary napkins are traditionally constituted by a first external layer permeable to physiological fluids, a central matrix essentially made of an absorbing material such as cloth, cotton, paper wadding or batts of cellulose fibre and a second external layer impermeable to physiological fluids and to aggregates formed by the physiological fluids with the absorbing material present in the central matrix. The central matrix is entrapped between both layers. The central matrix of diapers, originally essentially made of pads of fluffed cellulose pulp fibres, have over a time span of about 20 years gradually been substituted by synthetic absorbent polymers and by synthetic superabsorbent polymers in the form of a hard, dry, granular powder. A detailed description of such absorbent is given in Modem Superabsorbent Polymer Technology, by Frederic L. Buchholz and A. T. Graham, edited by Wiley-VCH, pages 1 to 16 which document is thereby incorporated by reference.
Pads of fluffed cellulose pulp fibres absorb about 12 grams of water whereas a superabsorbent polymer may absorb up to one thousand (1,000) grams of water per gram of polymer.
However such a high performance is only reached with solutions in distilled aqueous water. Such superabsorbents lose rapidly their performances in solutions with a high ionic content.
However superabsorbent polymers are not used alone, but typically used in admixture with at least one another material with absorbing properties, in order to improve the absorbing profile. For example, superabsorbent polymer granules are mixed with wood pulp fluff in diapers.
Those superabsorbent polymers mainly used commercially are cross linked, partially neutralized poly(acrylic acid) or graft copolymers such as partially neutralized starch-g-poly(acrylic acid) and partially neutralized poly(vinyl alcohol)-g-poly(acrylic acid). Others well-known superabsorbent polymers are hydrolyzed starches-g-poly(acrylonitrile).
Intensive searches have been performed in order to improve the absorbency of known synthetic and semi-synthetic superabsorbents. Thus U.S. Pat. No. 4,935,022 describes absorbent articles which utilize a particular type of stiffened cellulose fibers and a particular type and form of polymeric gelling agent particles to enhance the absorbency characteristics of such articles. In these articles, the gelling agent material, combined in particulate form of a certain size with stiffened cellulose fiber material, is primarily placed in a lower fluid storage layer of the absorbent core of the article. Such a fluid storage lower layer of the absorbent core is placed underneath an upper, generally larger, fluid acquisition/distribution layer which also contains stiffened cellulose fibers and gelling agent particles of a certain size. The gelling particles have a mass median particle size ranging from about 400 to 1680 microns. The mentioned gelling agent is a substantially water-insoluble slightly, partially neutralised polymer selected from hydrolysed acrylonitrile grafted starch, polyacrylates, maleic anhydride-based copolymers and combinations of these polymers therefor.
U.S. Pat. No. 5,047,023 describes an absorbent article wherein the deposition region of its absorbent member comprises a storage zone and a acquisition zone having a lower average density and a lower average basis weight per unit area than the storage area. The acquisition zone is positioned toward the front of either the absorbent member or the absorbent article so that the acquisition zone may most effectively and efficiently rapidly acquire discharged liquids. The absorbent member comprises a mixture of a hydrophylic fibrous material and discrete particles of absorbent gelling material having a particle size distribution so as to enhance the absorbent capacity and acquisition rate of the absorbent member. The particles of the absorbent gelling material are selected to have a mass median particle size greater than or equal to about 400 microns with the amounts of very large and very small particles preferably kept below certain minimum concentrations. As suited absorbent gelling material particles are those already mentioned in U.S. Pat. No. 4,935,022. Mentioned as preferred absorbent gelling material are hydrolized acrylonitrile grafted starches, acrylic acid grafted starches, polyacrylates, maleic anhydride copolymers and combination thereof.
U.S. Pat. No. 5,061,259 describes absorbent structures and absorbent gelling agent compositions suitable for use in disposable absorbent articles. The absorbent structures comprise hydrophylic fiber material and nonfragile particles of polymeric gelling agent. The gelling agent particles incorporated into such structures are selected to have a mass median particle size ranging from about 400 to 700 microns, with no more than about 16% by weight of said particles having a particle size less than 200 microns and no more than about 16% by weight of said particles having a particle size greater than 1000 microns. The gelling agent particles are preferably nonfragile particles of hydrogel-forming polymeric gelling agent with a specific granulometry and comprise a specific amount of the grafted starches already mentioned in U.S. Pat. No. 5,047,023 and in U.S. Pat. No.4,935,022.
In spite of their advantages, the above mentioned synthetic or semi-synthetic superabsorbents, also called xe2x80x9csuper slurperxe2x80x9d, exhibit major drawbacks.
Most of the synthetic superabsorbents are not biodegradable and semi-synthetic superabsorbents are generally only slightly biodegradable.
Moreover, due to their hardness and to their chemical nature, particulates of synthetic superabsorbents and particulates of semi-synthetic superabsorbents generate irritability of intimate body parts.
Allergic reactions to synthetic or semi-synthetic superabsorbents, occuring inter alia when granulates of synthetic superabsorbents come in contact with mucous membranes, are commonly reported.
Furthermore, semi-synthetic and synthetic superabsorbents are hygroscopic. This tendency to absorb moisture represents a major drawback. Particularly for applications wherein a long retention time of the absorbed fluid is required.
Finally and in having regard to new environmental regulations, there is an increasing need for biodegradable hygiene products like diapers. Such a need resulted over the past years in intensive searches for new biodegradable hypoallergenic and non-hygroscopic polymeric materials with a high absorbency and with good stability in a wide pH range.
A first object of the present invention is a particulate absorbent, for the absorption of liquids, comprising particles of glass-like polysaccharides and/or of particles of glass-like polysaccharides occluding, in their internal structure, at least one surfactant. The glass-like polysaccharides are characterized in that their particles have a specific granulometry. These particulate absorbent is biodegradable, non-hygroscopic, hypoalergenic and stable on a wide pH range.
A second object of the present invention is a process for preparing those particulates absorbent according to the first object of the invention wherein the glass-like polysaccharides occlude at least one surfactant, in their internal structure.
A third object of the present invention is an absorbing, particularly a biodegradable, non-hygroscopic and hypoallergenic absorbing composition comprising, in specific ranges, a particulate absorbent according to the first object of the invention, an insoluble carboxymethylcellulose and a high viscosity carboxymethylcellulose.
A fourth object of the present invention is an absorbing, particularly a biodegradable, hypoallergen and non-hygroscopic absorbing, composition comprising, in specific ranges: a particulate absorbent according to the first object of the invention, a xanthane gum and a guar gum.
A fifth object of the present invention is an absorbent combination of at least one particulate absorbent according to the first object of the invention and/or a absorbent composition according to the third or to the fourth object of the present invention with a suitable carrier.
A sixth object of the present invention is constituted by:
breast pads (nursing pads),
food pads,
diapers (disposable and non disposable infant diapers, training pants),
adult incontinence products (personal pads, bed pads, briefs),
feminine hygiene products (tampons, sanitary napkins), and
surgery and surgical pads or bandages,
in which a particulate absorbent according to the first object and/or an absorbing composition according to the third and/or to the fourth object of the present invention has been incorporated.
In general, in accordance with the present invention, there is provided a particulate absorbent, for the absorption of liquids, comprising particles of glass-like polysaccharides wherein said particles have a size of up to 620 xcexcm. In general, in accordance with the present invention, there is also provided a particulate absorbent, for the absorption of liquids, comprising particles of glass-like polysaccharides occluding, in their internal structure, at least one surfactant wherein said particles have a size of up to 620 xcexcm. In accordance with the present invention, the particles may be at least 70% by weight of a glass-like type structure. In accordance with the present invention the particles may have a size in the range of from 5 to 500 xcexcm.
In general, in accordance with the present invention, there is further provided an absorbent combination comprising a particulate absorbent as defined herein with a carrier.
The first object of the present invention is a particulate absorbent, for the absorption of liquids, comprising polysaccharide particles. The polysaccharide particles may comprise particles of glass-like polysaccharides, particles of glass-like polysaccharides occluding, In their internal structure, at least one surfactant or mixtures thereof, said particles:
having a size of up to 620 xcexcm;
being at least 70% by weight of a glass-like type structure; and
being
30 to 45% by weight of a size comprised between 620 and 420 xcexcm;
35 to 55% by weight of a size comprised between 420 and 210 xcexcm; and
5 to 25% by weight of a size up to 210 xcexcm.
In accordance to the present invention, the polysaccharide may preferably be based on an amylaceous polysaccharide such as an amylose or an amylopectine or on a mixture of amylose and amylopectine.
A suited starting polysaccharide is a native unmodified polysaccharide, preferably a native unmodified starch, more preferably a grade A starch.
The grade A starch is preferably a wheat starch but may also be a corn, barley, potato, rye, manioc or milo or any other starch sources.
Essential features of grade A wheat starch are represented in following Table I.
This starch is mainly constituted by granulates with a lentil form and with a size ranging from 25 to 40 xcexcm.
Suited starting grade A wheat starches are those commonly used in paper, food, textile and fermentation industries. Moreover grade A wheat starches in their native as well in their glass-like form are commonly used as ingredient in food industry.
In accordance with the present invention, the particles of the glass-like polysaccharide and the particles of the glass-like polysaccharide occluding, in their internal structure, at least one surfactant, may have a size ranging from 5 to 500 xcexcm (e.g. a size of about 300) xcexcm.
The mean of the polysaccharide particles present in the particulate absorbent according to the invention may preferably ranges from 150 to 500 xcexcm and may more preferably be about 300 xcexcm.
The method used for determining the size of said polysaccharides present in the particulate absorbent also name sieving method is defined as following:
each of six sieves of, according to US Standard, 30 mesh, 40 mesh, 50 mesh, 60 mesh, 100 mesh and 170 mesh are tarred,
100 grams of the sample is laid down on the first (30 mesh) sieve,
the fraction of the sample which is not retained by the first sieve falls into the second (40 mesh),
such a the selection process is repeated for each sieve,
each sieve is mechanically waved for 20 minutes and then tarred again, then the rate of particles retained on each sieve is calculated for 100 grams of the initial sample.
The standard deviation was calculated from 10 batches corresponding to the production of 218 lots over 3 years. The 10 standard deviation were calculated with the formula:   S  =            ∑              xe2x80x83            ⁢                        (                      f            ⁡                          (                              x                -                                  x                  _                                            )                                )                2                    n      -      1      
Wherein
f is the frequency of the result (for example 16% of particles have a size comprised between 250 and 420 microns),
x is the central value of the class (comprised between 250 and 420 microns preferably about 350 microns),
{overscore (x)} is the mean distribution of the lot and n is the number of results (100%).
The standard deviation is the average of these 10 standard deviations and the given range is the range between the lower standard deviation and the highest standard deviation.
The standard deviation of the particles of polysaccharides preferably ranges from 100 to 120 microns. According to a most preferred embodiment of the invention the standard deviation is about 110 microns.
The surfactant which is occluded in the internal structure of the glass-like polysaccharide is preferably an ionic surfactant comprising a linear alkyl moiety i.e. an ionic surfactant with a long alkyl linear chain. Mixtures of various surfactants are also suited in the meaning of the invention. As examples of suitable anionic surfactant with a long linear chain are alkyl carboxylates, cationic alkyls ammonium, alkyl sulfonates and alkyl phosphates with at least 11 carbon atoms. Preferably the long linear chain (i.e. the linear alkyl moiety comprises or) has from 12 to 20 carbon atoms. More particularly adapted in the meaning of the invention is a surfactant selected in the group constituted by fatty acid salts such as sodium stearate.
The moisture content of the glass-like polysaccharide is up to 13%.
The selected particles of glass-like polysaccharides of the invention are obtained by screening of the particles of a glass-like polysaccharide.
Said glass-like polysaccharides may be partially crystallized. They have, at least 70%, more preferably at least 80%, and according to the best mode 100% of a glass-like type structure.
The latter glass-like polysaccharides (for example, glass-like starch) absorbent are further characterized by their elementary composition, which elementary composition comprises:
from 33 to 40 weight per cent of carbon;
from 53 to 59 weight per cent of oxygen;
from 6.6 to 7.5 weight per cent of hydrogen;
less than 0.15 weight per cent of sulfur;
less than 0.6 weight per cent of chloride; and
residuals,
the weight per cent being expressed by total weight of said glass-like polysaccharide (for example, glass-like starch).
Residuals means nitrogen, sodium, calcium and phosphor ions or any other unidentified compounds, unidentified materials or mixture thereof.
The glass-like polysaccharides (for example, glass-like starches) according to the invention, as determined by Infrared Spectroscopy conducted by using KBr as reference, comprises up to 3, preferably up to 2, more preferably about one molecule of water for each sugar unit of said polysaccharide.
A preferred family of glass-like polysaccharide (for example, glass-like starch) according to the invention is constituted by those glass-like polysaccharide (for example, glass-like starch) absorbent having the 3 (three) following intensive infrared bands respectively at:
1649xc2x15 cmxe2x88x921;
3446xc2x15 cmxe2x88x921; and
3504xc2x15 cmxe2x88x921,
which bands characterise the presence of water in the polymeric structure.